Re: [PATCH] mm: reset migratetype if the range spans two pageblocks

[Xishi Qiu <qiuxishi@huawei.com>]

On 2015/10/16 18:06, Xishi Qiu wrote:

> __rmqueue_fallback() will change the migratetype of pageblock,
> so it is possible that two continuous pageblocks have different
> migratetypes.
> 
> When freeing all pages of the two blocks, they will be merged
> to 4M, and added to the buddy list which the migratetype is the
> first pageblock's.
> 
> If later alloc some pages and split the 4M, the second pageblock
> will be added to the buddy list, and the migratetype is the first
> pageblock's, so it is different from the its pageblock's.
> 
> That means the page in buddy list's migratetype is different from
> the page in pageblock's migratetype. This will make confusion.
> 
> However,if we change the hotpath, it will be performance degradation,
> so any better ideas?
> 

How about using get_pfnblock_migratetype() to get the pageblock's
migratetype first, and compare them?

Thanks,
Xishi Qiu

> Signed-off-by: Xishi Qiu <qiuxishi@huawei.com>
> ---
>  mm/page_alloc.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 48aaf7b..5c91348 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -726,6 +726,9 @@ static inline void __free_one_page(struct page *page,
>  	list_add(&page->lru, &zone->free_area[order].free_list[migratetype]);
>  out:
>  	zone->free_area[order].nr_free++;
> +	/* If the range spans two pageblocks, reset the migratetype. */
> +	if (order > pageblock_order)
> +		change_pageblock_range(page, order, migratetype);
>  }
>  
>  static inline int free_pages_check(struct page *page)



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